1. Field of the Invention
The present invention relates to a thin-film magnetic head for reading and writing signals as magnetic field intensity of a magnetic recording medium, and more particularly to the structure of and the method for fabricating a thin-film magnetic head of CIP configuration, and further, to a thin-film magnetic head wafer, and to a head gimbal assembly and a hard disk device which utilize the thin-film magnetic head.
2. Description of the Related Art
The progression of hard disk drives to ever-greater magnetic recording density has reached a level in which the mass production of devices in the 100-Gbpsi class is now being targeted. In response to this progression to higher densities, magnetic heads which employ a GMR (Giant Magnetoresistive) sensor are being used as reproduction elements. In particular, GMR sensors which use spin-valve (SV) films exhibits great change in resistance to the sense current which flows in the sensor for reading the record of a recording medium and can provide a magnetic head of higher sensitivity. An SV film is a laminated film which is formed by sandwiching a nonmagnetic intermediate layer between a ferromagnetic layer in which the direction of magnetization is fixed in one direction (hereinbelow, also referred to as a “pinned layer”) and a ferromagnetic layer in which the direction of magnetization changes according to the external magnetic field generated by the recording medium (hereinbelow, also referred to as a “free layer”). In an SV film, the direction of magnetization of the free layer forms a relative angle with respect to the direction of magnetization of the pinned layer according to the external magnetic field, and the spin-dependent scattering of conduction electrons changes according to this relative angle, thereby giving rise to change in magneto-resistance. A magnetic head detects this change in magneto-resistance to read the magnetic information of the recording medium.
The mainstream of read sensors has been a CIP (Current In Plane)-GMR sensor, in which a sense current flows parallel to the layer surfaces. Although there is a recent push for the development of CPP (Current Perpendicular to the Plane)-GMR sensors in which the sense current flows perpendicular to the layer surfaces and TMR sensors which employ TMR (Tunnel Magneto-Resistance) films to cope with even higher recording densities, the importance of CIP-GMR sensors remains unchanged.
FIG. 1 shows a partial perspective view of a read head portion of a conventional thin-film magnetic head. Thin-film magnetic head 101 may be a head dedicated for reading, or may be an MR/inductive composite head which further includes a write head portion. MR sensor 102 is sandwiched between lower magnetic shield 103 and upper magnetic shield 109 with its end portion arranged at a position which confronts recording medium D. Lower insulating layer 104 is further provided between MR sensor 102 and lower magnetic shield 103, and upper insulating layer 108 is provided between MR sensor 102 and upper magnetic shield 109 (in contrast to FIG. 1, MR sensor 102 and upper insulating layer 108 are actually in contact). The surface which confronts recording medium D will hereinbelow also be referred to as air bearing surface ABS. Lateral layers 105a and 105b are provided on the sides of MR sensor 102, and as shown by the solid black arrow in FIG. 1, sense current 122 flows parallel to the surface of stack of MR sensor 102. The magnetic field of recording medium D at the position confronting MR sensor 102 changes with the movement in the direction T of recording medium D which is shown by the white arrow in FIG. 1. MR sensor 102 is able to read the magnetic information which is written to each magnetic domain of recording medium D by detecting this change in the magnetic field as the change in electrical resistance of sense current 122 which is obtained by the GMR effect.
FIG. 2 shows a sectional view taken along the line A-A in FIG. 1, i.e., seen from air bearing surface ABS of MR sensor 102. MR sensor 102 is formed by laminating lower ferromagnetic layer 121, non-magnetic layer 122, and upper ferromagnetic layer 123 in that order, and lateral layers 105a and 105b are provided on both sides of these layers. Upper insulating layer 108 and upper magnetic shield 109 are then laminated in that order over these layers.
Lateral layers 105a and 105b are each composed of bias layer 106 and lead layer 107. Bias layer 106 is composed of a soft magnetic layer and an antiferromagnetic layer (not shown). Lead layer 107 functions as an electrode for the flow of sense current 122. A protective layer (not shown) may in some cases be provided over this layer. Bias layer 106 exerts a bias magnetic field upon MR sensor 102. Bias layer 106 will be described in further detail hereinbelow.
In general, it is desirable for MR sensors such as CIP-GMR sensors to exhibit linear characteristics of change in resistance in response to change in the external magnetic field. For that purpose, detection of an external magnetic field is carried out while a bias magnetic field is applied to an MR sensor. In MR sensors of the prior art, a hard magnetic layer has been used as the magnetic material which produces the bias magnetic field. However, the trend toward higher recording densities of the recording medium has been requiring write elements and MR sensors which can cope with narrower tracks. In the 100-Gbpsi class device which is close to mass production, the width of the free layer must be reduced to the order of 100 nm, a reduction which requires a major advance in microprocessing technology. However, there are limits to microprocessing technology, and microprocessing of this order may lead to a degradation of yield. Given these circumstances, it has been found that the use of an exchange bias layer in which the hard magnetic layer is replaced by a laminate of a soft magnetic layer and an antiferromagnetic layer enables a reduction of the effective track width for reading for the same free layer width, and is thus effective for achieving higher recording densities. Although the mechanism for this effect is not clear enough, it is believed that a form of side-shield effect is brought into play due to the use of the soft magnetic layer. The term “bias layer” in the present specification refers to an exchange bias layer.
Bias layer 106 and lead layer 107 have substantially identical planar shape and are laminated with bias layer 106 below and lead layer 107 above, and as shown by lateral layers 105a and 105b in FIG. 1, are formed to a deep position from air bearing surface ABS. In the present specification, the word “deep” is used with regard to the distance in the direction perpendicular to air bearing surface ABS. The same holds true for “height.” Bias layer 106 and lead layer 107 are formed to a deep position for reasons for the fabrication process and for the purpose of suppressing the series resistance of lead layer 107. In other words, to produce an MR sensor according to the prior art, lower ferromagnetic layer 121, non-magnetic layer 122, and upper ferromagnetic layer 123 are laminated in that order over the entire surface of the substrate, following which portions of these layers are replaced by a pair of bias layers 106 and lead layers 107 which are separated by track width TW. A resist is then formed, and the rear portions (as seen from air bearing surface ABS) of lower ferromagnetic layer 121, non-magnetic layer 122, and upper ferromagnetic layer 123 are removed to form MR sensor 102 of a prescribed MR height. At this stage, if lead layer 107 is not sufficiently thick or if a protective layer of sufficient thickness is not present on lead layer 107, the upper portion of lead layer 107 is removed in the vicinity of MR sensor 102. This removal results in an increase in the series resistance of lead layer 107 to the sense current, preventing increase in sensitivity. Therefore, lead layer 107 is made sufficiently thick or a protective layer of sufficient thickness is formed on lead layer 107 simultaneously with bias layer 106 and lead layer 107. In such a configuration, lead layer 107 is protected and not reduced unnecessarily in the vicinity of MR sensor 102, and a sufficient cross-sectional area is ensured. As a result, the simultaneously formed bias layer is also formed to the same deep position in substantially the same “U” form as the lead layer 107.
However, an MR sensor which employs exchange bias layers suffers from the following problems. Various measurements are made in the fabrication steps of a thin-film magnetic head to check performance, one of these tests being the Quasi-Static Test (QST). This test is performed by simulating the actual environment of use as a hard disk device before final assembly. More specifically, a uniform magnetic field which is generated by a magnetic field generating means is applied from the outside in place of the magnetic field of a recording medium to measure and appraise the various characteristics of a magnetic head which is in the process of fabrication.
However, the magnetic field applied in this test, which is in the range of several ten thousands of A/m (several 100 Oe), is significantly greater than the magnetic field exerted upon the product in an actual environment. The exchange bias layer is more prone to fluctuation with respect to the external magnetic field than a hard magnetic layer, and when subjected to such a strong magnetic field, the direction of magnetization of the layer is partially disrupted, whereby the exchange bias layer is unable to properly exert a bias magnetic field upon the MR sensor, and the effective track width is consequently enlarged (degraded).
This point is next explained in greater detail. A measurement method known as the microtrack profiling method is used to appraise the effective track width. In the microtrack profiling method, the head is off-tracked (shifted in the direction of track width) with respect to the written track to erase either both sides or one side of the track and thereby form a track width having approximately ⅕- 1/10 of the written track width. The read head is then off-tracked on this narrow track and the change in the reproduction output is measured. The reproduction output normally assumes a bell-shaped form which takes the track center as its apex when the amount of off-tracking is taken on the transverse axis and the reproduction output is taken on the vertical axis, as shown in FIG. 3A. The amount of off-tracking which corresponds to the half-width of this reproduction output is taken as the effective track width.
However, when subjected to a large magnetic field by, for example, QST, the peak not only diverges from the track center, but maximum points also emerges at positions other than the peak, as shown in FIG. 3B. In addition, exposure to external magnetic fields occur in various situations other than QST. These maximum points are referred to as side lobes, and side lobes tend to degrade the resolution in the direction of track width, to increase the effective track width, and consequently, to interfere with higher recording densities.
Forming bias layers in the narrowest possible rectangular shape is believed to be effective for suppressing the occurrence of side lobes. This effect is believed to occur probably because the shape anisotropy of the bias layer stabilizes the bias layer against strong magnetic fields in the direction of depth, and particularly against magnetic fields caused by QST. A number of bias layers having such long and narrow shapes have been disclosed (for example, refer to the specification of Japanese Patent Laid-Open Publication No. 2001-351208).
In the prior art, however, if the lead layer is formed to a deep position to suppress the series resistance of the lead layer, the bias layer is also formed to a deep position, and the suppression of side lobes which results from forming a long and narrow bias layer therefore cannot be expected. On the other hand, when the bias layer is formed in a long and narrow shape to solve the problem of side lobes, the lead layer is reduced in the vicinity of the MR sensor, and this configuration increases the series resistance to the sense current.
Thus, in the prior art, a technique which is capable of satisfying the contradictory demands of suppressing the occurrence of side lobes and suppressing the series resistance of the lead layer has not yet been disclosed. However, these contradictory demands must be satisfied to achieve higher recording densities in the future.